Light induced catalytic intramolecular hydrofunctionalization of allylphenols mediated by porphyrin rhodium(iii) complexes

Photochemical conversion of CO to C1 and C2 products mediated by porphyrin rhodium(II) metallo-radical complexes

Unimolecular reduction and bimolecular reductive coupling of carbon monoxide (CO) represent important ways to synthesize organic feedstocks. Reductive activation of CO through open-shell pathways, though rare, can help overcome the barriers of many traditional organometallic elementary reactions that are hard to achieve. Herein we successfully achieve the unimolecular reduction of CO to (TPP)RhCH2OSiR1R2R3 (TPP = 5,10,15,20-tetraphenylporphyrin), and the release of products CH3OSiR1R2R3, TEMPO-CH2OSiR1R2R3 and BrCH2OSiR1R2R3 in near-quantitative yield under visible light (420-780 nm), which involves radical formation from Rh-C bond homolysis. Bimolecular CO reductive coupling products, (TPP)RhCOCH2OSiR1R2R3, are then obtained via a radical mechanism. Subsequent treatment with n-propylamine, BrCCl3 or TEMPO under thermal or photochemical conditions afford small-molecule bimolecular reductive coupling products. To the best of our knowledge, homogeneous systems which reductively couple CO under photochemical conditions have not been reported before. Here, the use of an open-shell transition metal complex, that delivers more than one kind of small-molecule CO reductive coupling products bearing different functional groups, provides opportunities for useful CO reductive transformations.

Site-Isolated Rhodium(II) Metalloradicals Catalyze Olefin Hydrofunctionalization

Rh(II) porphyrin complexes display pronounced metal-centered radical character and the ability to activate small molecules under mild conditions, but catalysis with Rh(II) porphyrins is extremely rare. In addition to facile dimerization, Rh(II) porphyrins readily engage in kinetically and thermodynamically facile reactions involving two Rh(II) centers to generate stable Rh(III)-X intermediates that obstruct turnover in thermal catalysis. Here we report site isolation of Rh(II) metalloradicals in a MOF host, which not only protects Rh(II) metalloradicals against dimerization, but also allows them to participate in thermal catalysis. Access to PCN-224 or PCN-222 in which the porphyrin linkers are fully metalated by Rh(II) in the absence of any accompanying Rh(0) nanoparticles was achieved via the first direct MOF synthesis with a linker containing a transition-metal alkyl moiety, followed by Rh(III)-C bond photolysis.

Reductive C(sp3)-C(sp3) homo-coupling of benzyl or allyl halides with H2 using a water-soluble electron storage catalyst

This paper reports the first example of a reductive C(sp3)-C(sp3) homo-coupling of benzyl/allyl halides in aqueous solution by using H2 as an electron source {turnover numbers (TONs) = 0.5-2.3 for 12 h}. This homo-coupling reaction, promoted by visible light, is catalysed by a water-soluble electron storage catalyst (ESC). The reaction mechanism, and four requirements to make it possible, are also described.

Recent applications of porphyrins as photocatalysts in organic synthesis: batch and continuous flow approaches

In this review we present relevant and recent applications of porphyrin derivatives as photocatalysts in organic synthesis, involving both single electron transfer (SET) and energy transfer (ET) mechanistic approaches. We demonstrate that these highly conjugated photosensitizers show increasing potential in photocatalysis since they combine both photo- and electrochemical properties which can substitute available metalloorganic photocatalysts. Batch and continuous-flow approaches are presented highlighting the relevance of enabling technologies for the renewal of porphyrin applications in photocatalysis. Finally, the reaction scale in which the methodologies were developed are highlighted since this is an important parameter in the authors' opinion.

Synthesis and applications of rhodium porphyrin complexes

A review on rhodium porphyrin chemistry, ranging from synthesis and properties to reactivity and application.